Config improvements

• Do not send empty settings
• Settings search
• Add missing settings from config.exs
• Add error handling
• Add previews when uploading images
• Make Submit button sticky
• Add ability to send empty or null values

mentioned in issue #34 (closed)

This and the related backend issue pleroma#1441 (closed) are our highest priorities right now for AdminFE related work

Did we do all of these things but forget to check the boxes and close the issue?

marked the checklist item Do not send empty settings as completed

marked the checklist item Add error handling as completed

marked the checklist item Add previews when uploading images as completed

marked the checklist item Add ability to send empty or null values as completed

marked the checklist item Make Submit button sticky as completed

marked the checklist item Add missing settings from config.exs as completed

mentioned in merge request !102 (merged)

closed via merge request !102 (merged)

mentioned in commit 343f9506

mentioned in commit e392d482